Vehicle-lang

* Shadowing of declaration names by local variables is no longer allowed.

* Added JSON backend target to command-line interface

* Fixed bug when compiling to verification queries where `if` statements that when lifted reduced to trivial assertions were causing a crash.

* Fixed bug when compiling to verification queries where the error "Could not eliminate variable X" was occasionally thrown.

* Fixed bug where reconstructing counter-examples from Marabou would sometimes crash.

* Improved command-line output from the `vehicle verify` command.

* Added warnings when quantified variables aren't related by equalities to network input and outputs.

* Asymptotically significant speedup when compiling specifications with very large
tensors in them and a corresponding reduction in size of the `.vcl-plan` files being generated.

* Fixed bug where disjunctions were being evaluated incorrectly.

Command-line changes

* The `compileAndVerify` command has been merged into the `verify` command.
If the `specification` argument for the `verify` command is a folder containing a `.vclp` file then the behaviour remains identical to the `verify` command of the previous version.
If it points to `.vcl` file then the behaviour is that of the removed `compileAndVerify` command.

* The names of the loss function values for the `verify` command's `target` argument have changed from the format `LossFunction-X` to the format `XLoss`, e.g. `LossFunction-Godel` to `GodelLoss`.

Bug fixes

* Fixed bug where `vehicle compile --help` gave the wrong list of available values for the `target` argument.

* Fixed bug where sometimes using literal numbers on one side of an inequality would fail to type-check (e.g. `forall (i : Index 5) . i <= 1`).

* Fixed issue where compiling an expression with an `if` in to Marabou would fail if one of the branches was trivial.

Errors

* Improved informativeness of error messages thrown when attempting to verify properties with multiple network applications.

* Improved error reporting when Marabou is automatically terminated by the OS (e.g. runs out of memory)

General enhancements

* The verification plan files generated by `vehicle compile -t MarabouQueries` command have been
changed from `verificationPlan.vcle` to the more readable `.vcl-plan`.

* The proof cache files generated by `vehicle verify` command have been
changed from `X.vclp` to the more readable `.vcl-cache`.

Command-line interface changes

* The command `vehicle verify` now requires you to point at the folder generated by the previous
`vehicle compile` command, rather than the verification plan file within it, and therefore the
parameter `--verificationPlan` has been changed to `--queryFolder`.

i.e. an old command `vehicle verify --verificationPlan=my/project/queries/verificationPlan.vcle` now
becomes `vehicle verify --queryFolder=my/project/queries`.

Language changes

* Added additional overload for division operator `/`. Dividing two `Nat`s together now results in
a `Rat`.

Bug fixes

* Fixed erroneous error message generated when giving inferable parameters an unsupported type.

* Fixed erroneous evaluation of when dividing two rationals together.

* Fixed bug where the compiler would sometimes hang when reading `.vclo` files created with an
older version of Vehicle.